Method of producing hydrocarbons from a subsurface formation by thermal treatment



May 28, i968 J. OFFERINGA 333559 METHOD OF PRODUCING HYDROCARBONS FROM A SUBSURFACE FORMATION BY THERMAL TREATMENT Filed SEPT.. 29, 1966 FIG` 2 NVENTORI JAN OFFER! GA HIS AGENT United States Patent O 3,385,359 METHOD F PRODUClNG HYDRGCARBONS FRM A SUBSURFACE FURMATHUN BY THERMAL TREATMENT Jan Offeringa, Edmonton, Alberta, Canada, assigner to Sixeil Oil Company, New York, NSY., a corporation of Delaware Filed Sept. 29, 1966, Ser. No. SSZ-S Claims priority, application Canada, Mar. 18, 1966, 955,177 S Claims. (Cl. 166--2) The present invention relates to thermal means for producing hydrocarbons from subsurface tar sand formations in which the hydrocarbons are in a non-flowable highly viscous state. More particularly, the present invention relates to primary recovery by thermal means of hydrocarbons and tars from subsurface tar sand formations in which the recoverable materials are in a highly viscous state having a mean viscosity of at least 5,000 centipoises and generally above 10,000 centipoises.

Various methods have been proposed for the recovery of highly viscous hydrocarbons from subsurface formations such as by injection of hot fluids or in situ combustion with various degrees of success. However, such means have not been successful in recovering essentially immobile hydrocarbons from subsurface tar sands and conventional hot water or steam soaking of underground oil-containing formations as described in US. Patents 1,237,139 and 3,027,942 have not proved economically desirable or successful when applied to recovery of highly viscous hydrocarbons and tars from formations under discussion.

1t has now been discovered that relatively immobile hydrocarbons having a mean viscosity of at least 5,000 centipoises in subsurface tar sand formations can be effectively and economically recovered by reducing the viscosity of said hydrocarbons and tars to a flowable and fluid state by penetrating said formation with at least one well and thermal treating the recovery zone as follows (1) injecting through said well into the hydrocarbon recovery or production zone of said tar sand formation a hot liquid at a temperature higher than the temperature of the formation being treated; (2) interrupting the hot liquid injection after a predetermined time sufficient to allow the formation to be heated and the viscosity of the hydrocarbon reduced to somewhat llowable or mobile states, (3) removing said hot liquid from the formation and injecting therein through the same injection well a hot condensable vapor or in injecting said hot condensable vapor without removal of the hot liquid, (4) interrupting the injection of the hot condensable vapor and (5) recovering the hydrocarbons and tars in a mobile and owable state from the well in communication with the production or recovery zone of the subsurface tar sand formation by a suitable means such as by simply pumping off the well.

By the expression hot liquid there is meant a hot liquid such as hot Water having a temperature which is higher than the temperature of the formation to be treated.

By the expression hot condensable vapor is meant a condensable vapor such as steam which can be wet, dry or superheated having a temperature which is higher than the temperature of the formation to be treated.

The well may be closed in for some time after the hot liquid has been injected, in order to promote the heat exchange between the liquid and the formation.

The pressure of the formation is preferably reduced to below the pressure of the overburden after the injection of hot liquid has been interrupted and before injecting the hot condensable vapor; since this step improves the ice mobility of the essentially immobile hydrocarbons and tars as they exist in the formation prior to the hot water injection which is virtually immobile under formation conditions.

One aspect of the invention is a method of producing tar from an underground tar sand formation in which at least one well penetrates, said tar having a viscosity of at least 5000 centipoises at formation temperature, comprises the following sequence of steps:

(a) injecting hot water into the formation through the well;

(b) Interrupting the injection of hot water until the formation is substantially heated and the tars rendered similarly mobile; l

(c) injecting steam into the formation through the same well;

(d) Interrupting the injection of steam and the tar heated to a mobile and flowable state, and

(e) Opening the well for the production tar.

Prior to steam injection, the water can be removed and the pressure in the formation reduced to below the overburden pressure, namely to about atmospheric pressure by venting the well.

The invention will be further described by way of example, with reference to an embodiment of the invention, of which the FIGURE l drawing schematically shows a vertical section taken over a well penetrating the subsurface.

The tar-containing formation 10, such as tar sand, is enclosed in vertical direction by baserock 12 and caprock or overburden 13 which are impermeable. The well 14 penetrates the ground surface 25 through the caprock 13 and in the formation 10.

The well 14 is provided with the usual equipment such as casing, wellhead, liner, tubing, which equipment has, however, been omitted from the drawing for the sake of simplicity.

A conduit system, comprising the conduits 15, 16, 17, 18, 19 and the valves 20, 21, 22, 23 communicates at one side thereof via conduit 15 with the wellhead of the well 14, and at the other sides respectively with a source of hot water (not shown) via conduit 16, a source of steam (not shown) via conduit 17 and a storage (not shown) for the produced products via conduit 19.

The source of hot water, the source of steam as well as the storage and any other equipment which may be used for controlling the flow of fluids through the conduits and treating the fluids to be injected as well as the fluids being produced, are not described in detail since this type of equipment is known per se.

After the well 14 has been drilled and completed, and the wellhead thereof has been brought into communication with the abovementioned conduit system, the valve 20 in conduit 16 and the valve 22 in the conduit 18 are opened and hot water is allowed to flow from the hot water source (not shown) to the formation 10 through the conduits 16, 18 and 1S, and the well 14. It will be clear that valves 21 and 23 are then in the closed position. If desired, the formation 10 may be fractured as indicated at 2.4, to reduce the pressure required to inject the water into the formation 10.

The temperature and the amount of hot water to be injected into the formation 10 are so chosen so as to be able to mobilize the tar present the part of the formation 10 directly surrounding the well 14 as well as in those parts of the formation 10 which are at a more remote distance from the well 14. Small temperature increases of, say, 45 F. (25 C.) will be sufficient to reduce the viscosity of the tar between and 96.5% in a viscosity range of 10,000 to 1,000,000 centipoiscs under formation conditions thereby transferring tar from an essentially immobile state under formation conditions to a relatively viscous but mobile state.

On interruption of the injection of the hot water into the formation (by closing the valve 2?) and opening the well 14 for production (by opening the valve 23 in the conduit 1.9), tar-if anywill be produced at a very small rate only since the degree to which the tar has been mobilized is insufficient to overcome the resistance to flow which this tar encounters in the formation part directly surrounding the well 14, such that it will flow in a radial dire-ction to the well 14 at rates which make the production of tar economically acceptable. Even if the production of tar is tried to be improved by installing a well pump in the Well 14 to lift the tar to the surface, the rate of tar production will be far below the required economic limits. However, by opening the Well 14 after the injection of the hot water, its temperature will be lower over that of hot water injection ternperature and it will be driven out of the formation. This generally occurs in formations having immobile tar present in the pore space thereof. The removal of the water after it has had an opportunity to thermally soak the formation is advantageous since the pore space not occupied by water is filled with steam during the steam injection step and thereby more steam can be injected resulting in better and more efficient thermal soaking of the formation thereby mobilizing the immobile tar.

Thus by the steam injection step, the resistance to flow which will be encountered by the tar when tiowing through the formation part directly surrounding the well 14, is decreased drastically 'by injecting steam into the formation 10 via the conduit 15. During this steam treatment the valves 21 and 22 are open and the valves and 23 are closed.

Due to the radial tiow pattern of the tar during production thereof, the iiow velocity of the tar (and consequently the resistance met by the iiow) is smaller in the formation parts more remote from the well than in the formation part directly surrounding the well. Consequently, for a given amount of heat available to be injected into the formation, the maximum recovery of tar will be obtained if the formation part directly surrounding the well is heated to a temperature higher than the more remote parts of the formation, since this decreases the viscosity of the tar greatly just around the well where the resistance to iiow is highest, and only moderately (just enough to mobilize the tar) at the formation parts where the resistance to flow is smallest.

A desirable temperature profile in radial direction with respect to the well 14 can be obtained by the present method by applying hot water for moderately heating the more remote formation parts, and steam for intensively heating the formation part directly surrounding the well.

During the recovery of the high temperature tar through the well 14, low temperature tar will iiow into the formation part directly surrounding the well 14. Since the temperature of the sand of this formation part is higher than the temperature of the iniiowing tar, this tar will be heated which reduces the viscosity thereof as well as the resistance to flow encountered thereby. This latter is very desirable since the velocity of the tar fiow increases at smaller distances from the well which would result in a higher resistance to flow were it not for the simultaneously occurring decrease in viscosity.

By the procedure of the present invention, heat is generally withdrawn from the immediate surroundings of the well 14, of the formation 10 and it will cool down, whereby the temperature of the tar, present in that part will drop, which results in an increase in the viscosity and a simultaneous increase of the resistance to flow. The production rate drops consequentially, and the production is to be stopped before it falls below the economic limit. Thereafter, a new amount of steam is injected into the formation part directly surrounding the well, provided that the temperature of the more remote parts of the formation is still sufficiently high to warrant the required mobility of the tar present therein. Thus, various steam treatments of the formation (alternated by production periods) may be carried out subsequent to a single hot water treatment.

After the water injection and before the steam injection, the formation pressure may be reduced by removing relatively cold water from the formation via the well 14. Any tar which is produced together with the Water during this period, is produced at a rate which is outside the economic limits.

During the actual production periods, the heat content of the more remote parts of the formation with respect to the well may be droppped to a value so that the viscosity of tar present therein increases to a value at which an economic production of the tar is no longer possible. Under such conditions, these parts of the formation can be subjected once more to a hot water treatment, followed by a number of steam treatments alternated by production periods.

It will be appreciated that the invention is not limited to any particular type of pattern of wells in which the thermal treatment can be carried out. If a number of wells are drilled, one half of the Wells may be steam treated after being thermally hot water soaked and the other half can be producing (and vice versa).

If desired, as shown in FIGURE 2, the hot liquid injected through the well 14 into the formation 10 may be circulated through this formation to a second well 14a in communication through fracture 24 through which well 14a the liquid is drained (at a temperature lower than the injection temperature) from the formation 10. After a sufficient amount of liquid has been circulated through the formation to mobilize the tar present between these two wells fracture communicated 14 and 14a, the injection of the hot liquid is interrupted, and the injection of steam through well 14 followed by the production of tar via the well 14a is carried out subsequently, in a manner equal to the one as has previously been described with reference to FIGURE 1. If desired, the formation area surrounding the second well 14a may be treated simultaneously with the formation area surrounding the iirst well 14, by injecting the formation area surrounding the first well 14, by injecting steam followed by the production of tar. The steps of injecting steam, interrupting this injection and opening the well for production may be carried out simultaneously in the two wells 14 and 14a. In another way, however, the steam treatment and tar production are carried out such that the period of steam injection into the one well (14) and the period of production of tar from the formation via the other Well (14a) substantially coincide. Thus, a single steam generator can 'be used which alternately communicates with its steam outlet to one of the two wells. In the recovery of tars shown in FIGURE 2 from well 14a which is in communication with well 14 through fracture 24, valve 15b in conduit 15a and valve 25a in conduit 25 should be open and Valve 23 in conduit 19 should be closed.

Any suitable agent (such as a surface-active agent) for increasing the mobility of the tar may be added to the hot liquid and/or to the hot condensable vapor.

The injection of the hot water and the steam may be at any level within the formation 19. Since the injected hot water will seek the formation layers having the smallest resistance, the injected hot water will fiow through the layers of the formation 10, having the highest water saturation, thereby heating adjoining formation layers which have lower water saturations.

When applying a fracture 24 in the formation part around .the well 14, for decreasing the resistance to iiow during the injection of the hot water, this fracture is preferentially horizontal. When the zone in the neighborhood of the fracture 24 has been depleted, a new fracture may be made at a diiferent level, and the whole process may be repeated to deplete the zone adjoining this new fracture. When using two or more wells for carrying out the present method and circulating liquid between these wells during the preheating stage for mobilizing the tar, such fracture may extend between these wells.

After each injection of a hot iuid, the well may be closed in for a certain period so as to allow the hot fluid to transfer its heat to the formation and the contents thereof. If desired, the well pressure may be reduced after the closed-in period following the hot liquid injection period, by opening the well, and producing cold liquid from the formation.

l claim as my invention:

1. Method of producing hydrocarbons from a subsurface tar sand formation containing immobile hydrocarbons in which at least one well penetrate-s, comprising:

(a) injecting only hot water into the formation through a well penetrating the formation;

(b) interrupting the injection of the hot water;

(c) thereafter injecting steam into the formation through the same well;

(d) interrupting the injection of the hot condensable vapor; and

(e) thereafter opening the well for production of hydrocarbons.

2. Method according to claim 1 wherein the well is closed in between steps b and c.

3. Method according Ito claim 1 wherein between the steps b and c the well is opened for reducing the pressure in the pore space of the formation.

4. Method according to claim 1 wherein between the steps b and c the well is first closed in and thereafter opened for reducing the pressure in the pore space of the formation.

5. Method according to claim 1 wherein the liquid injected into the formation during step a is circulated to a second well via which it is drained from the formation, and wherein the steps c, d and e are also carried out in this second well.

6. Method according to claim 1 wherein the liquid injected into the formation during step a is circulated to a second well from which it is drained from the formation and wherein the step c, the step d and the step e are carried out simultaneously in the first well and the second Well.

7. Method of producing tar from an underground tar sand formation in which at least one well penetrates, said tar having a viscosity of at least 5G60 centipoises at formation temperature, said method comprising the following steps:

(a) injecting only hot water into the formation through a well penetrating the tar formation;

(b) interrupting the injection of hot water;

(c) thereafter injecting ste-am into the formation through the same well;

(d) interrupting the injection of steam; and

(e) thereafter opening the well for the production of tar.

8. Method of producing tar from an underground tar sand in which at least one well penetrates, the tar having a viscosity of at least 5000 centipoises at formation temperature, which method comprises:

(a) injecting only hot water through the well penetrating the tar sand and raising the temperature in the formation parts not directly surrounding the well;

(b) interrupting the injection of hot water;

(c) thereafter injecting steam into the tar sand through the well to raise the .temperature in the formation part directly surrounding the well to a value higher than the temperature of the more remote formation parts;

(d) interrupting the injection of steam; and

(e) thereafter opening the well and producing tar therefrom.

References Cited UNITED STATES PATENTS 2,862,558 12/1958 Dixon 166-40 2,909,224 lG/1959 Allen.

3,126,961 3/1964 Craig et al. 166-40 3,221,813 12/1965 Closmann et al 166-40 X 3,259,186 7/1966 Dietz 166-40 X 3,266,569 8/1966 Sterrett 166-2 3,288,214 11/1966 Winkler 166-40 3,292,702 12/1966 Boberg 166-40 3,349,849 10/1967 Closmann 166-40 3,351,132 11/1967 Dougan et al. l66-40 X STEPHEN I. NOVOSAD, Primary Examiner. 

1. METHOD OF PRODUCING HYDROCARBONS FROM A SUBSURFACE TAR SAND FORMATION CONTAINING IMMOBILE HYDROCARBONS IN WHICH AT LEAST ONE WELL PENETRATES, COMPRISING: (A) INJECTING ONLY HOT WATER INTO THE FORMATION THROUGH A WELL PENETRATING THE FORMATION; (B) INTERRUPTING THE INJECTION OF THE HOT WATER; (C) THEREAFTER INJECTING STEAM INTO THE FORMATION THROUGH THE SAME WELL; (D) INTERRUPTING THE INJECTION OF THE HOT CONDENSABLE VAPOR; AND 